Waning of post vaccinial allergy after neonatal BCG vaccination

Tuberculin sensitivity or post vaccinial allergy (PVA) is widely used as an indicator of successful BCG vaccination. The protection conferred by BCG vaccination, the duration of post-vaccinial allergy and the relationship between the two remain a subject of controversy. The present study was conducted with the aim of finding the duration of PVA and evaluate the need for revaccination. One thousand newborns were given BCG under controlled conditions and followed up for PVA by serial PPD (5TU) injection at 3, 6, 12, 24, 30 and 36 months. An induration of 5 mm or less was recorded as negative and no subsequent testing was done. At 3 month, all the infants were given PPD and 95.3% showed a positive response. The positivity rate declined significantly (p < 0.01) to 19% by 3 years of age. A statistically significant (p < 0.01) fall in the mean PPD induration size was also noted. At 3 months, the mean induration size was 10.68 mm but by 3 years it had decreased to 3.86 mm. The distribution of PPD size also showed that with the increase in age, there was a shift towards the smaller size. At 3 years of age, none of the children had an induration of more than 10 mm. The booster effect due to repeated PPD testing was seen in a small percentage and only at 6 and 12 months test. Subsequently no increase in PPD induration was noted. Sex of the child did not influence the PPD induration size significantly (p > 0.05). At 3, 6 and 12 months of age, significant correlation between BCG lesion and PVA was noted, the co-efficient of correlation being 6.(ABSTRACT TRUNCATED AT 250 WORDS)